Lithium extraction process and apparatus

ABSTRACT

A method of extracting lithium from a lithium-bearing material including: 
     (i) mixing the lithium-bearing material, gypsum, a sulfur-containing material, and a calcium-containing material and forming a feed mixture having a moisture content of at least 20 wt %; 
     (ii) drying the feed mixture to form a dried mixture having a moisture content of less than 20 wt %; 
     (iii)roasting the dried mixture and forming a roasted mixture including a water-soluble lithium compound; and 
     (iv) leaching lithium from the water-soluble lithium compound and forming a lithium-containing leachate by mixing the aqueous solution and the water-soluble lithium compound.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority to,PCT/U52020/62855 entitled “A Lithium Extraction Process and Apparatus,”filed Dec. 2, 2021. Said application is incorporated herein fully byreference.

FIELD OF INVENTION

The invention relates to a process and an apparatus for extractinglithium from a lithium-bearing material.

In particular, although by no means exclusively, the invention relatesto a process and an apparatus for extracting lithium from low gradelithium-bearing material such as waste material from borates mining orclay formations.

BACKGROUND

Lithium is used to make batteries for a variety of applicationsincluding electric cars, cameras and mobile phones.

Lithium is obtained by either extracting lithium-containing salts fromunderground brine reservoirs or mining lithium-containing rock.

One example of lithium-containing rock is in deposits in borates mines,with lithium being in waste rock/clay and tailings generated from theborates mining and recovery process.

Low value gangue material typically ends up in a tailings dam or in astacked heap. The tailings and stacked heaps have low concentrations oflithium that cannot be extracted economically at the present time. Thelithium in the tailings and stacked heaps, whilst low grade, is apotential asset that may be unlocked economically later with currenttechnology or with improving technology. The amounts of tailings andwaste rock generated during mining can be significant and, hence, thepotential lithium value can be significant.

Lithium is also present, typically in low concentrations, in clayformations and, to date, it has been challenging to extract lithium fromthese formations in an economically viable way.

There are a number of known processes for extracting lithium fromlithium-containing materials.

However, it has been challenging to extract lithium in a practical andeconomic way from low grade lithium bearing material such as tailings,waste rock and clay formations described above.

It would be desirable for a process to extract lithium from low gradelithium-bearing material.

The above description is not an admission of the common generalknowledge in Australia or elsewhere.

SUMMARY OF INVENTION

The present invention provides a process for extracting lithium fromlithium-bearing material, particularly low grade lithium-bearing wastematerial.

The lithium-bearing material may be a sediment-hosted deposit.

The sediment-hosted deposit may be waste tailings obtained from anindustrial processing plant such as a primary process plant, a boricacid processing plant or a borates mine. The waste tailings may havebeen subjected to acid or water leaching. The sediment-hosted depositmay comprise lithium bearing clay minerals.

The lithium bearing clay minerals may be processed or treated clay forexample clay minerals found in the waste material from a processingplant which may have been processed, for example, by leaching.

The lithium bearing clay minerals may be virgin clay such as untreatedor natural clay, for example obtained from clay formations.

Examples of clay minerals include smectites such as hectorite and/ormontmorillonite, Bigadic clays, and lithium bearing illite with orwithout lithium zeolites.

The lithium-bearing material may be material in which lithium isassociated with high concentrations of sodium, aluminum, silicon and/orboron. Typically, the lithium-bearing material comprises 8-32 wt % ofsodium, aluminum, silicon, potassium and/or boron per kg oflithium-bearing material. Suitably, the lithium-bearing material is aboron-containing ore.

The expression “low grade” refers to a lithium concentration rangingfrom 1-3 g/kg of lithium-bearing material.

The present invention provides a method of extracting lithium from alithium-bearing material including:

-   -   (i) mixing the lithium-bearing material, gypsum, a        sulfur-containing material, and a calcium-containing material        and forming a feed mixture having a moisture content of at least        20 wt %;    -   (ii) drying the feed mixture to form a dried mixture having a        moisture content of less than 20 wt %;    -   (iii)roasting the dried mixture and forming a roasted mixture        including a water-soluble lithium compound; and    -   (iv) leaching lithium from the water-soluble lithium compound        and forming a lithium-containing leachate by mixing the aqueous        solution and the water-soluble lithium compound.

The present invention also provides a method of extracting lithium froma lithium-bearing material including:

-   -   (i) mixing the lithium-bearing material, gypsum, a        sulfur-containing material, and a calcium-containing material        and forming a feed mixture having a moisture content of at least        20 wt %;    -   (ii) drying the feed mixture to form a dried mixture having a        moisture content of less than 20 wt %;    -   (iii)supplying the dried mixture to a roaster;    -   (iv) roasting the dried mixture in the roaster and forming a        roasted mixture including a water-soluble lithium compound;    -   (v) supplying the water-soluble lithium compound to a leach        tank;    -   (vi) supplying an aqueous solution to the leach tank; and    -   (vii)leaching lithium from the water-soluble lithium compound        and forming a lithium-containing leachate by mixing the aqueous        solution and the water-soluble lithium compound in the leach        tank.

One advantage of the present invention is that it provides a lithiumextraction process that can extract value from waste material, forexample waste rock and tailings, generated from a variety of industrialprocesses including, but not limited to, borates mining.

Another advantage of the present invention is that it provides a lithiumextraction process that reduces the operating cost of the process. Theroasting step in a known lithium extraction method is recognised as akey driving factor for operational costs. The present invention replacespart of the gypsum used in the known roasting step with afunctionally-equivalent substance (i.e. the sulfur-containing materialincluding elemental sulfur or an alkali metal sulfate, such as sodium orpotassium sulfate) that can be generated on-site or in-situ to reducethe operating cost.

A further advantage of the present invention is that it provides aprocess that uses an environmentally benign substance, water, in theextraction process instead of highly acidic solutions. This is achievedby a roasting step in which Li-silicate from clays is converted intoLi2SO4 which is water soluble.

The applicant also discovered that roasting wet feed mixture having amoisture content of at least 20 wt % has the potential to increaselithium recovery by at least 5%. Testwork showed that lithium recoveryusing roasted feed material could exceed 80% whereas dry mixing ofunroasted material typically had a lithium recovery of about 70%.

The sulfur-containing material may be either or a combination of analkali metal sulfate and elemental sulfur.

The alkali metal sulfate may be either or a combination of sodiumsulfate and potassium sulfate. Suitably, the alkali metal sulfate issodium sulfate.

The alkali metal sulfate may be obtained from an effluent waste streamof a processing plant.

Suitably, the alkali metal sulfate is obtained from boric acid plantliquor or tailings pond.

The calcium-containing material may be either or a combination ofcalcium carbonate such as limestone or dolomite, and lime. Thecalcium-containing material may be substituted with magnesium carbonate.

The calcium-containing material may have maximum particle size of 88microns (−170 mesh). Suitably, the maximum particle size is 74 microns(−200 mesh). More suitably, the maximum particle size is 63 microns(−230 mesh).

The method may include a comminution step to form calcium-containingmaterial having a maximum particle size of 88 microns (−170 mesh).

The method may include screening the calcium-containing material to formcalcium-containing material having a maximum particle size of 88 microns(−170 mesh).

The gypsum may have maximum particle size of 88 microns (−170 mesh).Suitably, the maximum particle size of gypsum is 74 microns (−200 mesh).More suitably, the maximum particle size of gypsum is 63 microns (−230mesh).

The method may include a comminution step to form gypsum having amaximum particle size of 88 microns (−170 mesh).

The method may include screening the gypsum to form calcium-containingmaterial having a maximum particle size of 88 microns (−170 mesh).

The mixing step may involve mixing wet lithium-bearing material withgypsum, a sulfur-containing material, and a calcium-containing materialand forming the feed mixture. Suitably, the wet lithium-bearing materialhas a water content ranging from 20-60 wt %. More suitably, the wetlithium-bearing material has a water content ranging from 40-50wt %.

Existing technology for extracting lithium from lithium-bearing materialtypically requires the feed material to be substantially dry (e.g. lessthan 10 wt % moisture) before they are mixed. It can be appreciated thatsuch technology is not appropriate for processing waste gangue material,for example, from a tailings pond because this material is usuallymoisture rich. Energy would have to be expended to dry the feed materialin preparation for the mixing step, often making the processuneconomically viable.

The mixing step may involve adding an aqueous solution, preferablywater, to lithium-bearing material having a water content of less than20 wt % to form the feed mixture.

The mixing step may form a mixture having a composition in which thegypsum: sulfur-containing material ratio is at least 1:1 (e.g. 1 kggypsum: 1 kg sodium sulfate).

Suitably, the amount of gypsum: sulfur-containing material ratio is atleast 2:1 (e.g. 2 kg gypsum: 1 kg sodium sulfate).

Suitably, the gypsum: sulfur-containing material ratio is at least 3:1(e.g. 3 kg gypsum:1 kg sodium sulfate).

Even more suitably, the gypsum: sulfur-containing material ratio is 7:3(e.g. 7 kg gypsum: 3 kg sodium sulfate).

The applicant has discovered that <30% substitution of gypsum with asulfur-containing material delivers lithium recoveries comparable togypsum-only mixtures but at reduced operating costs.

The applicant discovered that complete substitution of gypsum withsodium sulfate resulted in a lithium recovery of less than 25%.

The mixing step may form a mixture having a predetermined compositioncomprising lithium-bearing material: calcium-containing material:gypsum: sulfur-containing material at a ratio of lithium-bearingmaterial (1): calcium-containing material (0.4-0.8): gypsum (0.3-0.5):sulfur-containing material (0.1-0.3). Suitably, the mixing step forms amixture comprising lithium-bearing material: calcium-containingmaterial: gypsum: sulfur-containing material at a ratio of100:45-75:20-50:10-25.

The above ratios for calcium-containing material may apply to calciumcarbonate such as limestone or dolomite, and lime.

The above sulfur-containing material ratios are particularly suitablefor sodium sulfate. In this respect, a skilled person would understandthat adjustments may have to be made to the ratios if a differentsulfur-containing material, for example potassium sulfate, is used.

The mixing step may include mixing the feed mixture for a minimum of 5minutes. Suitably, the feed mixture is mixed for a minimum of 10minutes. More suitably, the feed mixture is mixed for minimum of 20minutes.

The mixing step may include mixing the feed mixture from 15-45 minutes.Suitably, the mixing step includes mixing the feed mixture for 15minutes.

The mixing step may be performed at a speed ranging from 10-80 rpm.Suitably, the mixing step is performed at a speed ranging from 15-70rpm.

The mixing step may be performed in a high shear intensity mixer.Suitably, the high shear intensity mixer is an Eirich high intensitymixer.

Suitably, the mixing step forms a homogeneous mixture. It was determinedthat controlling the mixing speed and/or time enables the formation ofthe homogeneous mixture and may facilitate the formation of granules (orpellets) for roasting.

The mixing step may include drying of the homogeneous mixture to reduceits moisture content to less than 15 wt %, suitably less than 10 wt % toform a granulated mixture.

The drying step may reduce the moisture content of the feed mixture andform a granulated mixture. Suitably, the drying step reduces themoisture content of the feed mixture to less than 15 wt %, suitably lessthan 10 wt %.

Suitably, the granules have a mean diameter less than 30 mm. Moresuitably, the granules have a mean diameter less than 20 mm. Even moresuitably, the granules have a mean diameter less than 10 mm.

The granules may have a mean diameter ranging from 5-20 mm.

The granules may have a moisture content of less than 15 wt %. Suitably,the granules may have a moisture content of less than 10 wt %. Moresuitably, the granules may have a moisture content of less than 5-10 wt%.

The method may include a granulating step to process the mixture intogranules. The granulating step may be part of the mixing step orseparate to the mixing step.

The granulating step may include drying the feed mixture to reduce itsmoisture content to less than 20 wt %. Suitably, the granulating stepincludes drying the feed mixture to reduce its moisture content to amaximum of 15 wt %. More suitably, the granulating step includes dryingthe feed mixture to reduce its moisture content to a maximum of 10 wt %.

The roasting step may be performed at a roasting temperature rangingfrom 800-1,000° C.

Suitably, the roasting step is performed at a roasting temperatureranging from 850-950° C.

More suitably, the roasting step is performed at a roasting temperatureranging from 857-925° C. Even more suitably, the roasting step isperformed at a roasting temperature of 900° C.

The roasting step may be performed for a roasting time period rangingfrom 15 mins to 2 hours. Suitably, the roasting step is performed for aroasting time period ranging from 20 minutes to 1 hour.

The roasting time period is the time period during which the mixture isexposed to the roasting temperature. This roasting time period may bedifferent to the residence time of the mixture in a kiln or furnacewhere the mixture may not be exposed to the roasting temperature for itsentire residence time in the kiln or furnace. For example, the mixturemay be exposed to a varying temperature profile as it is conveyedthrough a kiln. In this example, the roasting time period when themixture is conveyed to a location in the kiln where is it exposed to theroasting temperature.

The roasting step may be performed at a roasting temperature rangingfrom 800-1,000° C. for a roasting time period ranging from 15 minutes to2 hours.

When the mixture is roasted in a kiln, the roasting step is performed ata roasting temperature of 850° C. for a roasting time period rangingfrom 20 minutes to 1 hour. In the kiln, the mixture goes through adrying process in a first zone wherein it will gradually reach thetarget temperature. Once it reaches the target temperature, the materialis exposed to the target temperature for 20 to 30 minutes.

When the mixture is roasted in a crucible placed in a furnace, theroasting step is performed at a roasting temperature of 900° C. for aroasting time period of 1 hour.

Sulfur-containing material including sodium, potassium and calciumsulfates may be generated during the roasting step. It can also beappreciated that unreacted sulfur-containing material may also bepresent in the roasted material. As this material is an ingredient ofthe roasting recipe, recycling this material back into the mixer reducesfeed material costs.

As such, the method may include a step of adding sulfur-containingmaterial from the roasting step to the mixing step.

The method may include a step of adding sulfur-containing material,typically in the form of sodium sulfate, obtained from crystallisationof the lithium-containing leachate to the mixing step. Thissulfur-containing material can be used as a reagent to partially replacegypsum in the mixing step.

The water-soluble lithium compound may be lithium sulfate.

The method may include a step of crushing the water-soluble lithiumcompound before the leaching step. Suitably, the crushing step involvesreducing the particle size of the water-soluble lithium compound to1,000-5,000 μm (1-5 mm). More suitably, the particle size of thewater-soluble lithium compound ranges from 1,000-3,000 μm (1-3 mm).

The leaching step may include adding an aqueous solution to the roastedmixture to form a slurry having a solids content ranging from 20-50 wt%, suitably, a solids content ranging from 25-45 wt %, more suitably, asolids content ranging from 30-40 wt %.

The method may include counter-current leaching of the lithium from thewater-soluble lithium compound. Suitably, the method may include two ormore counter-current leaching steps. Other appropriate leaching methodsinclude co-current leaching, use of drum filters and simple leaching.

The countercurrent leaching step may form a lithium-containing leachatehaving a lithium concentration of at least 300 ppm.

In this specification, the aqueous solution used in the leaching stepmay have a pH ranging from 6.5-7.5. Suitably, the pH of the aqueoussolution is 7.

It can be appreciated that while it is preferred that the aqueoussolution used in the process has a pH of 7, the process can also utilisewater from a variety of sources which may contain minerals or substancesthat causes the pH to deviate from 7 by ±0.5.

The leaching step may be performed at a temperature less than 60° C.Suitably, the leaching step is performed at a temperature less than 50°C. More suitably, the leaching step is performed at a temperatureranging from 20-40° C.

The method may include filtering the slurry to remove undissolved solidssuch as calcium carbonate and clay. Suitably, the filtering stepgenerates a lithium-containing leachate having a lithium concentrationof at least 2,000 ppm.

The method may include concentrating the leachate.

The concentrating step may involve evaporating part of the leachate toform a concentrated leachate having a lithium concentration of at least3,000 ppm.

Suitably, the concentrating step involves evaporating part of theleachate to form a concentrated leachate having a lithium concentrationof at least 4,000 ppm.

More suitably, the concentrating step involves evaporating part of theleachate to form a concentrated leachate having a lithium concentrationof at least 4,500 ppm.

The concentrating step may result in the formation of impuritiesincluding calcium and sodium salts and/or particulate matter includingthenardite, glaserite, glauberite, or anhydrite.

The method may include filtering the concentrated lithium-containingleachate to remove the impurities.

The filtered concentrated lithium-containing leachate may be processedvia a series of steps to form lithium carbonate. The applicant hasdeveloped a process of forming lithium carbonate from the filteredconcentrated lithium-containing leachate which is the subject ofInternational patent application

PCT/U52020/062844 filed on the same day as the present application bythe same applicant, the disclosure of which is incorporated in itsentirety.

The method may include recycling alkali metal sulfate (e.g. sodiumsulfate) formed during the roasting step to supplement thesulfur-containing material in the feed material.

The invention also provides an apparatus to perform the previouslydescribed method.

In one form, the invention provides an apparatus for extracting lithiumfrom a lithium-bearing material comprising:

-   -   (i) a mixer configured to receive and mix lithium-bearing        material with gypsum, a sulfur-containing material, and a        calcium-containing material and form a feed mixture having a        moisture content of at least 20 wt %;    -   (ii) a dryer configured to dry the feed mixture and form a dried        mixture having a moisture content of less than 20 wt %;    -   (iii) a roaster configured to receive and roast the dried        mixture and form a roasted mixture including a water-soluble        lithium compound; and    -   (iv) a leach tank configured to form a lithium-containing        leachate from the water-soluble lithium compound using an        aqueous solution.

The apparatus may be located near or connected to a source oflithium-bearing material and be configured to receive this material.

The apparatus may include a comminutor for grinding or crushing thecalcium-containing material to form calcium-containing material having amaximum particle size of 88 microns (−170 mesh). Suitably, thecomminutor forms calcium-containing material having a maximum particlesize of 74 microns (−200 mesh).

The apparatus may include screen or a filter to form calcium-containingmaterial having a maximum particle size of 88 microns (−170 mesh).

The apparatus may include a comminutor for grinding or crushing thegypsum to form gypsum having a maximum particle size of 88 microns (−170mesh). The comminutor may be a mill such as a ball mill.

The apparatus may include screen or a filter to form gypsum havingmaximum particle size of 88 microns (−170 mesh).

The mixer may include an impeller or rotor that is configured to mix thefeed mixture at a speed ranging from 10-80 rpm. Suitably, the mixer maybe a high shear intensity mixer. More suitably, the high shear intensitymixer is an Eirich high intensity mixer.

The mixer may be connected to a tailings pond to receive thelithium-bearing material.

The mixer may be connected to a boric acid plant to receive at leastpart of the sulfur-containing material such as an alkali metal sulfate.Suitably, the mixer is configured to receive an alkali metal sulfatefrom boric acid plant liquor or tailings pond. More suitably, the mixeris connected to a crystalliser that is configured to separate sodiumsulfate from waste material generated by the boric acid plant.

The mixer may be configured to dry and granulate the feed mixture.Suitably, the granules have a mean diameter less than 30 mm. Moresuitably, the granules have a mean diameter less than 20 mm. Even moresuitably, the granules have a mean diameter of 10 mm or less. Yet evenmore suitably, the granules have a mean diameter ranging from 5-10 mm.

The mixer may be configured to receive alkali metal sulfate generatedduring the roasting step.

The dryer may be integral to the mixer.

The dryer may be used to reduce the moisture content of the mixedmaterial in the mixer (e.g. the homogeneous mixture) to less than 20wt%, suitably less than 10 wt %.

The dryer may inject hot air to reduce the moisture content of the feedmixture. The air has a temperature ranging from 50-120° C. Suitably, theair has a temperature ranging from 60-110° C. More suitably, the air hasa temperature ranging from 80-110° C.

The apparatus may include a granulator to process the mixture from themixer into granules.

The granulator may process the mixture from the mixer into granulesranging from 5-20 mm. Suitably, the granules range from 5-10 mm.

The apparatus may include a crystalliser to separate thesulfur-containing material such as sodium sulfate from the roastedmixture from the roaster. This allows the sulfur-containing material tobe recycled back to the mixer.

The crystalliser may be configured to perform flash crystallisation.Flash crystallisation is a process which enables the crystallisationtemperature to be reached rapidly.

The mixer may be connected to the crystalliser to receive the separatedsulfur-containing material.

The roaster may be a calciner or a kiln.

The roaster may be connected to the mixer to recycle alkali metalsulfate (e.g. sodium sulfate) formed during the roasting step tosupplement the sulfur-containing material in the feed material.

The apparatus may include a crusher to reduce the particle size of theroasted mixture from the roaster to 1,000-5,000 μm (1-5 mm). Suitably,the particle size of the roasted mixture ranges from 1,000-3,000 μm (1-3mm).

The leach tank may form part of a counter-current leaching circuit.

The apparatus may comprise three leach tanks arranged in series.

The leach tank may include a filter to generate a lithium-containingleachate having a lithium concentration of at least 2,000 ppm.

The apparatus may include an evaporator to evaporate at least part ofthe leachate from the leach tank to form a concentrated leachate havinga lithium concentration of at least 3,000 ppm.

The evaporator may include a filter to remove impurities from theconcentrated lithium-containing leachate.

BRIEF DESCRIPTION OF DRAWINGS

The invention is hereinafter described by way of example only withreference to the accompanying drawings, wherein:

FIG. 1 is a process flow diagram according to one form of the invention.

FIG. 2 is a process flow diagram illustrating the process of forming thegranulated mixture according to one form of the invention.

FIG. 3 is a process flow diagram illustrating the process of forminglithium carbonate according to one form of the invention.

DETAILED DESCRIPTION

The applicant has carried out research and development work on a knownmethod of extracting lithium from lithium-bearing deposit. The knownmethod includes roasting the deposit with calcium carbonate and gypsumand acid leaching the roasted mixture to extract the lithium.

Disadvantages of this process include the use of externally sourcedreagents including environmentally hazardous acid. In addition, acidleaching may not be adapted to extract lithium from material containinglow concentrations of lithium because of the relatively unselectivenature of acid leaching compared to water leaching.

The applicant has discovered that a gypsum/sulfur-containing materialmixture can reduce operating costs without losing the efficiencyassociated with traditional calcium carbonate: gypsum recipes ingenerating water-soluble lithium compounds. The applicant alsodiscovered that a gypsum/alkali metal sulfate mixture provides a moreefficient roasting process compared to a mixture that excludes gypsum.

The applicant also realised that boric acid plants produce sodiumsulfate as a waste product which can be routed to the apparatus of thepresent invention to reduce the amount of sodium sulfate that have to bepurchased or synthesised for the present invention.

The applicant further realised that the roasting step may producein-situ sodium sulfate which can be routed to the apparatus of thepresent invention to further reduce the amount of sodium sulfate thathave to be purchased or synthesised for the present invention.

As a result of these realisations, the applicant has developed anapparatus for extracting lithium from a lithium-bearing material inaccordance with the present invention. The apparatus 10 as shown in FIG.1 comprises a mixer in the form of an Eirich mixer 12, a roaster in theform of calciner 14, and a leach tank 16. It can be appreciated that theEirich mixer can be replaced with any high intensity mixer.

The apparatus 10 is located near or connected to a source oflithium-bearing material and is configured to receive this material.Examples of suitable lithium-bearing material sources include a tailingspond of a borates mine or clay formations.

Suitably, the apparatus 10 is also located near or connected to a sourceof an alkali metal sulfate such as sodium sulfate.

The sodium sulfate and lithium-bearing material may be obtained from thesame source. For example, the apparatus 10 may be connected to thetailings pond of a boric acid processing plant to receive thelithium-bearing gangue and connected to a sodium sulfate-containingeffluent stream of the same plant to receive sodium sulfate.

The apparatus may include a hopper 18 to hold the lithium-bearinggangue. The gangue may be dry or wet. In this specification, wet ganguehas a moisture content of at least 20 wt %.

When processing dry gangue, the hopper 18 is located over a vibratingpan (or screw) that feeds the dry gangue into an impact mill tocomminute the gangue. The impact mill in turn feeds the comminutedgangue onto a vibratory screen, preferably having a 40 mesh sieve size,that is positioned over hopper 18.

The hopper 18 stores the classified gangue before it is fed into themixer 12. In this embodiment, water may be added to increase themoisture content of the gangue to at least 20 wt %.

When handling wet gangue, the gangue from hopper 18 is transporteddirectly to the mixer 12.

The other feed material including a calcium-containing material such ascalcium carbonate and gypsum can also be stored in separate bins beforebeing fed into the mixer 12.

The mixer 12 is configured to receive inputs of lithium-bearingmaterial, a sulfur-containing material such as an alkali metal sulfateor elemental sulfur, gypsum and a calcium-containing material such ascalcium carbonate and mix these materials in specific proportionsaccording to a predetermined roasting recipe, for example the recipesdescribed in Tables 1 and 2 below, to form a homogeneous mixture whichis subsequently granulated. The mixer 12 may include or be connected toa dryer to reduce the moisture content of the mixed material and formthe granulated mixture.

A product outlet of the mixer 12 discharges the granulated mixture intoa discharge bin 42 for delivery to the calciner 14. In anotherembodiment, the granulated mixture is transported by some conveyingsystem (belt conveyor, screw conveyor, pneumatic conveying, etc) fromthe mixer 12 to the kiln.

Alternatively, the mixer may be connected to a granulator for receivingand granulating the mixed material from the mixer 12.

The granulator may include a dryer to dry the granulated mixture.

FIG. 2 provides a process flow diagram illustrating an apparatus forforming the granulated mixture. The apparatus comprises a mixer, in theform of an Eirich mixer 12, hopper 18 for storing lithium bearingmaterial, bin 20 for storing limestone (calcium carbonate), and bin 38for storing gypsum.

Reagents including sulfur containing material such as elemental sulfuror an alkali metal sulfate are stored in additional bins or silos beforebeing introduced into the mixer.

When mixing wet feed material including lithium-bearing gangue having amoisture content of at least 20 wt %, glauber salts and glaserite formedduring the crystallization step may be pumped from the process into themixer.

Dust collector 39 controls dust levels during the mixing process anddischarge bin 42 receives the granulated mixture.

The Eirich mixer 12 is configured via a conveyor system to receivelithium-bearing material in the form of gangue from a tailings pond of aborates mine or clay formations from hopper 18, limestone from bin 20and gypsum from bin 38. Typically, feed material comprises wet ganguehaving a moisture content ranging from 40-60 wt %, −200 mesh drylimestone and −200 mesh gypsum. Elemental sulfur or an alkali metalsulfate is delivered into the mixer 12 via a separate bin/silo.

The gangue, limestone, gypsum and the sulfur containing material aremixed under high shear intensity in the Eirich mixer for a minimum of 10minutes, typically 15-45 minutes to form a homogeneous mixture.

The apparatus further includes a heater/dryer 44 to reduce the moisturecontent of the mixed material to about 10 wt % or less.

Under the appropriate conditions, a granulated mixture comprisinghomogenous pellets ranging from 5-20 mm and having a moisture contentbetween 5-10% is formed. In some embodiments, the mixer may be connectedto a granulator to granulate the mixed material.

The granulated mixture is discharged into discharge bin 42 and deliveredto a calciner 14. In a continuous process, the granulated mixture isdischarged onto a conveyor and delivered to the calciner 14.

The calciner 14 converts the lithium-bearing material into awater-soluble lithium compound such as lithium sulfate.

A product outlet of the calciner 14 is connected to a feed inlet of aleach tank 16 to discharge the calcined material into the leach tank. Insome embodiments, the calciner 14 may be connected to a cooler to coolthe roasted mixture before it is delivered to the leach tank 16. Inthese embodiments, the cooler may be connected to a crusher to reducethe particle size of the roasted mixture to 1,000-5,000 μm (1-5 mm).

The crushed compound may be stored in a surge bin to hold the roastedmixture before it is directed to the leach tank 16.

The leach tank 16 is further connected to a water supply to receivewater for the leaching step.

The leach tank 16 is configured to enable countercurrent flow of thelithium-bearing feed material and water during leaching of thewater-soluble lithium compound to form a lithium-containing leachate.

The applicant discovered that countercurrent flow of the lithium bearingmaterial and water during the leaching process, along with a number ofoperating parameters, optimised the extraction of lithium from thelithium bearing material. However, co-current leaching may also beperformed.

The leach tank 16 may be temperature controlled to enable the leachingprocess to be performed at a predetermined temperature.

The leach tank 16 may include a filter 22 to remove any undissolvedsolids 23 formed during the leaching process. Other suitablesolid-liquid separation techniques may be used to remove undissolvedsolids formed during the leaching process, including centrifugation.

The leach tank 16 includes a product outlet which is connected to aninlet of evaporator 24.

A surge tank may be connected to the leach tank 16 to hold the filteredleachate before it is directed to the evaporator 24.

The evaporator 24 receives and concentrates the leachate from the surgetank or directly from the leach tank. Impurities such as calcite,thenardite, glaserite, glauberite, and anhydrite may precipitate duringthe evaporation process. The leach tank 16 may include another filter 22to remove the precipitates from the leachate to form a concentratedleachate 28 which can be directed downstream for further processing orstored for later use.

In operation, the apparatus according to the invention is connected to aborates processing plant 26. Feed material comprising lithium-containingwaste material, for example from a tailings pond or a stacked heap fromthe plant, is directed to a flotation circuit 30 to remove some of thenon-lithium bearing material from the waste material. Thelithium-bearing concentrate exiting the flotation circuit is thendirected towards a dryer 32 to reduce the water content of theconcentrate, preferably to 20-50 wt % before it is stored in a hopper18. Suitable examples of lithium-bearing material include wastelithium-bearing clay minerals include smectites such as hectorite and/ormontmorillonite, Bigadic clays, and lithium bearing illite with orwithout lithium zeolites that have been subjected to a variety oftreatment steps such as roasting in the processing plant. It wasdiscovered that feeding lithium-bearing material having a water contentranging from 20-50 wt % enhanced the roasting step because the watercontent improves the granulation of the feed material prior to roasting.

Separate bins may be used to store a sulfur-containing material such aselemental sulfur or an alkali metal sulfate, gypsum andcalcium-containing material such as calcium carbonate. The alkali metalsulfate may be sourced from an effluent stream typically containingsodium sulfate, from the same plant. In FIG. 2, bin 20 is used to storelimestone, bin 38 is used to store gypsum. Elemental sulfur or an alkalimetal sulfate is stored in another bin (not shown).

Each of the feed material may be comminuted or screened prior todelivery to their respective bins to limit their maximum particle sizes.For example, the calcium-containing material may be limited to a maximumparticle size of 88 microns (−170 mesh), the gypsum may be limited to amaximum particle size of 88 microns (−170 mesh) and thecalcium-containing material having maximum particle size of 88 microns(—170 mesh).

These bins are connected to the mixer in the form of a high shearintensity Eirich mixer 12 which receives these materials in specificproportions to form a mixture that will eventually be processed via aseries of intermediate steps to form a concentrated lithium-containingsolution of at least 4,000 ppm. The gypsum and calcium-containingmaterial are typically sourced externally. The calcium-containingmaterial can be substituted with magnesium carbonate, dolomite or lime.

The sulfur-containing material is used to replace part of the gypsum inthe roasting recipe. This reduces the need to commercially source gypsumand may repurpose the waste output from the borates processing plant.Importantly, this arrangement allows commercial value to be extractedfrom waste products from a boric acid processing plant which wouldotherwise have been discarded and reduces the reliance on externallysourced reagents. It also improves tailings pond management.

The gangue material may be directed to an impact mill and passed througha classification screen to obtain −40 mesh particles before being fed tothe Eirich mixer 12, particularly if the gangue material is dry.

The various components are fed into the Eirich mixer 12 based on apreselected recipe to form a mixture having a lithium-bearing material:calcium carbonate: gypsum: sodium sulfate ratio of 100:30-40:20:20.Another suitable recipe has a gypsum: sodium sulfate ratio of 7:3.

The feed mixture is mixed for 15-45 minutes at a speed ranging from15-70 rpm to form a homogeneous mixture. A heater is used to reduce themoisture content of the mixed material to about 10 wt % or less to forma granulated mixture comprising homogenous pellets ranging from 5-20 mmand having a moisture content between 5-10%.

In one embodiment, the dried mixture is processed in a granulator toform granules having a mean diameter ranging from 5-20 mm.

The granulated mixture is then directed to a calciner 14 for roasting ata temperature ranging from 857-925° C. for about one hour.

In one embodiment, the mixture may be mixed with water to facilitate thegranulation process. This step is typically used on dry feed materialhaving a water content of less than 20 wt %. Alternatively, a wetmixture having a water content of greater than 20 wt % may be feddirectly into the granulator.

Examples of suitable roasting recipes wherein the lithium-bearingmaterial is waste lithium-bearing clay material are reproduced in Tables1 and 2 below.

TABLE 1 Examples of predetermined roasting recipes for lithium-bearingclay including sodium sulfate Recipe No Clay Limestone Gypsum SodiumSulfate 1 100 45 40 10 2 100 45 45 15

In Table 1, the mixture is roasted at a roasting temperature of 900° C.for a roasting time period of 60 minutes.

TABLE 2 Examples of predetermined roasting recipes for lithium- bearingclay including sodium sulfate and/or elemental sulfur. System RecipeLimestone/ Sodium Elemental % Li recovery No Clay Lime Gypsum Sulfate SRecovery STD. DEV % 1 100 45 50 0 85.2 2.1 76.7 2 100 60 30 0 10 84.41.3 75.9 3 100 70 0 0 15 70.0 5.4 63.0 4 100 65 20 10 10 78.7 1.2 70.8 5100 75 0 25 10 73.5 2.8 66.1 6 100 45 40 10 78.0 2.3 70.2

This roasting step converts the lithium bearing material into awater-soluble form for a subsequent water leaching step.

Representative chemical equations of the roasting process are set outbelow (Crocker.L Lithium and its recovery from low-grade nevada clays[Report].-[s.l.]: Bureau of Mines, 1988).

Reaction (B) above produces sodium sulfate and/or potassium sulfatewhich can be recovered and returned to the Eirich mixer 12 to supplementthe source of alkali metal sulfate.

The roasted material is fed into the leach tank 16 in countercurrentflow to a leaching solution of water to leach lithium from the formedwater-soluble lithium compounds. The solids content of the roastedmixture in the leach tank ranges from 10-40 wt %, suitably about 20 wt%. The roasted mixture may be directed into a cooler before being fed tothe leach tank.

The water used in the leaching step is ideally at a pH of 7. However, itcan vary between 6.5-7.5 depending on the water source.

In some embodiments, the method may include a step of crushing theroasted material, including the water-soluble lithium compound, beforethe leaching step. This step may enhance the leaching process. Suitably,the crushed material has a particle size ranging from 1,000-5,000 μm.

The leaching step is performed at a temperature of less than 50° C. Theapplicant determined that a leaching temperature of about 50° C.optimised the leaching efficiency in view of the inverse relationship ofsolubility with temperature of lithium sulfate.

During the leaching step, any undissolved solids such as calciumcarbonate and clay are removed by filter 22. At this stage, the leachatetypically has a lithium concentration of at least 2,000 ppm.

The filtered leachate is then directed to an evaporator 24 to beconcentrated.

During the evaporating step, impurities in the form of calcium andsodium salts and particulate matter including any one or more ofthenardite, glaserite, glauberite, and anhydrite may be formed. Theseimpurities 25 are removed by filter 22 to form a lithium-containingleachate 28 having a concentration of at least 4,500 ppm. This leachatemay be further processed downstream via a series of steps to formlithium carbonate or stored for other uses.

One of these steps involves crystallisation of the lithium-containingleachate to remove further impurities from the solution. In oneembodiment, the waste material obtained from the crystallisation step isreturned to the flotation circuit 30 via stream 34 to recover lithiumfrom the crystallisation step impurities.

Another step during the production of lithium carbonate is a lithiumcarbonate precipitation step which generates a filtrate which can berecycled back to the evaporator via stream 36.

FIG. 3 provides a second process flow diagram including unit operationsfor processing the lithium-containing leachate 28 into lithiumcarbonate. In this embodiment, the leachate 28 is directed into acrystalliser 40. The filtrate from the crystalliser is transferred intoa chamber 43 to precipitate lithium carbonate which is sent intocentrifuge 45. The stream 36 obtained from the centrifuge 45 is returnedto the evaporator 24 while the raw lithium carbonate is processed inrefinery 46 into refined lithium carbonate which is subsequently driedand forms the final product 48.

In the claims which follow and in the preceding description of theinvention, except where the context requires otherwise due to expresslanguage or necessary implication, the word “comprise” or variationssuch as “comprises” or “comprising” is used in an inclusive sense, i.e.to specify the presence of the stated features but not to preclude thepresence or addition of further features in various embodiments of theinvention.

1. A method of extracting lithium from a lithium-bearing materialincluding: (i) mixing the lithium-bearing material, gypsum, asulfur-containing material, and a calcium-containing material andforming a feed mixture having a moisture content of at least 20 wt %;(ii) drying the feed mixture to form a dried mixture having a moisturecontent of less than 20 wt %; (iii) roasting the dried mixture andforming a roasted mixture including a water-soluble lithium compound;and (iv) leaching lithium from the water-soluble lithium compound andforming a lithium-containing leachate by mixing the aqueous solution andthe water-soluble lithium compound.
 2. A method of extracting lithiumfrom a lithium-bearing material including: (i) mixing thelithium-bearing material, gypsum, a sulfur-containing material, and acalcium-containing material and forming a feed mixture having a moisturecontent of at least 20 wt %; (ii) drying the feed mixture to form adried mixture having a moisture content of less than 20 wt %;(iii)supplying the dried mixture to a roaster; (iv) roasting the driedmixture in the roaster and forming a roasted mixture including awater-soluble lithium compound; (v) supplying the water-soluble lithiumcompound to a leach tank; (vi) supplying an aqueous solution to theleach tank; and (vii)leaching lithium from the water-soluble lithiumcompound and forming a lithium-containing leachate by mixing the aqueoussolution and the water-soluble lithium compound in the leach tank. 3.The method according to claim 1, wherein the sulfur-containing materialis either or a combination of an alkali metal sulfate and elementalsulfur.
 4. The method according to claim 3, wherein the alkali metalsulfate is either or a combination of sodium sulfate and potassiumsulfate.
 5. The method according to claim 1, wherein thecalcium-containing material is either or a combination of calciumcarbonate and lime.
 6. The method according to claim 1, wherein themixing step involves mixing lithium-bearing material having a watercontent ranging from 20-60 wt % with the gypsum, the sulfur-containingmaterial, and the calcium-containing material.
 7. The method accordingto claim 1, wherein the mixing step involves adding an aqueous solutionto a lithium-bearing material having a water content of less than 20 wt% to form the wet lithium-bearing material.
 8. The method according toclaim 1, wherein the mixing step forms a feed mixture in which thegypsum: sulfur-containing material ratio is at least 1:1.
 9. The methodaccording to claim 1, wherein the mixing step forms a feed mixturehaving a predetermined composition comprising lithium-bearing material:calcium-containing material: gypsum: sulfur-containing material at aratio of lithium-bearing material (1): calcium-containing material(0.4-0.8): gypsum (0.3-0.5): sulfur-containing material (0.1-0.3). 10.The method according to claim 1, wherein the drying step includesprocessing the mixture into granules having a mean diameter less than 30mm.
 11. The method according to claim 1, wherein the roasting step isperformed at a roasting temperature ranging from 800-1,000° C. for aroasting time period ranging from 15 minutes to 2 hours.
 12. The methodaccording to claim 1, including a step of reducing the particle size ofthe water-soluble lithium compound to 1,000-3,000 μm (1-3 mm).
 13. Themethod according to claim 1, wherein the leaching step includes addingan aqueous solution to the roasted mixture to form a slurry having asolids content ranging from 20-50 wt %.
 14. The method according toclaim 13, wherein the aqueous solution used in the leaching step has apH ranging from 6.5-7.5.
 15. The method according to claim 13, includingfiltering the slurry to generate a lithium-containing leachate having alithium concentration of at least 2,000 ppm.
 16. The method according toclaim 1, including evaporating part of the leachate to form aconcentrated leachate having a lithium concentration of at least 3,000ppm.
 17. The method according to claim 1, including recycling alkalimetal sulfate formed during the roasting step to supplement thesulfur-containing material in the feed mixture.
 18. An apparatus forextracting lithium from a lithium-bearing material comprising: (i) amixer configured to receive and mix lithium-bearing material withgypsum, a sulfur-containing material, and a calcium-containing materialand form a feed mixture having a moisture content of at least 20 wt %;(ii) a dryer configured to dry the feed mixture and form a dried mixturehaving a moisture content of less than 20 wt %; (iii)a roasterconfigured to receive and roast the dried mixture and form a roastedmixture including a water-soluble lithium compound; and (iv) a leachtank configured to form a lithium-containing leachate from thewater-soluble lithium compound using an aqueous solution.
 19. Theapparatus according to claim 18, including an evaporator to evaporate atleast part of the leachate from the leach tank to form a concentratedleachate having a lithium concentration of at least 3,000 ppm.
 20. Theapparatus according to claim 18, wherein the roaster is connected to themixer to recycle alkali metal sulfate in the roaster to the mixer.